Semiconductor wafer processing typically is carried out at vacuum, or sub atmospheric pressure. As process parameters become more stringent, the industry is moving towards single wafer processing tools and away from batch processing of multiple wafers in a chemical bath. This requires that the processing chamber or vessel be opened and closed for every wafer that is cycled thru the tool. Gate valves that comprise an up/down motion, and some attempts at sideways motion, are currently state of the art. The side motion is limited at best, some manufacturers using pneumatic actuation, others using cams, or just a slight angle orientation of the up/down axis to the chamber face to move a gate valve head into intimate contact with the processing chamber. Many gate valves seal internally to the valve assembly, the seal to the process chamber being an additional seal point.
Once the vacuum pumps are turned on in the process chamber, the area of the gate valve exposed to vacuum on the process chamber side and standard atmospheric conditions on the other side translate into a force directed from the higher pressure side of the gate valve to the lower pressure side of the pressure chamber. This force assists to compress the seal between the gate valve and the chamber (or gate valve internal sealing face). In a sense, the seal between the gate valve and the process chamber becomes sealed by the process being performed in the chamber. In this case, the pressure in the process chamber is lowered or brought to a vacuum, referred to as negative pressure.
Some newly developed processes for wafers operate at pressures higher than atmosphere. Conventional gate valves will not operate in such systems, as the process pressure will prevent the gate valve from sealing. Some processes, such as these operating under high-pressure conditions will cause a dangerous operating environment if conventional gate valves are used. Conventional gate valves will not operate in such systems.
There exists a need for a gate valve that operates in a positive pressure environment, which is a process in which the pressure within the process chamber is increased.